Topographic Distribution of UnCovered Areas (UCA) in Full Tone Flexographic Prints

Local unprinted areas of a full-tone printed substrate, UCA (uncovered areas), occur when incomplete ink transfer takes place during the printing process. This paper proposes a method for characterizing the substrate topography in the uncovered areas in a flexographic print. Fourteen graphic boards, printed using an IGT-F1 laboratory press, were analyzed with an integrated instrument consisting of the STFI grazing light topography characterization method (OptiTopo) and an UCA detection algorithm. The validity of the algorithm was verified by visual evaluation. The analysis of frequency distribution of UCA occurrence suggests a strong link between UCA occurrence and the topographic character of the substrate. A close inspection decisively indicates that surface depressions are the driving cause of uncovered areas. Frequency analysis and two different models of topographic thresholding were successfully tested as predictors of UCA occurrence.